Power Generator Dams

Most electric power is generated in large plants that use coal, gas, oil, or nuclear energy. Electric energy may also be obtained from waterpower. The roar of a waterfall suggests the power of water. Rampaging floodwaters can uproot strong trees and twist railroad tracks. When the power of water is harnessed, however, it can do useful work for man. Since ancient times man has put to work the energy in the flow of water. He first made water work for him with the waterwheel—a wheel with paddles around its rim. Flowing water rotated the waterwheel, which in turn ran machinery that was linked to it. Today, new kinds of waterwheels spin generators that produce electricity. Electricity from water-turned generators is called hydroelectric power.

Waterpower produces about 8 percent of the electricity used in the United States. It accounts, however, for only a fraction of the total energy used for mechanical power, heat, light, and refrigeration. Coal, petroleum, and natural gas supply most of the rest. Among water's virtues as a source of power is the fact that it can be used again after it supplies energy, while other energy sources are destroyed when they are used. Hydroelectric installations also supply added benefits to a region. For example, a dam built to provide a head for water turbines usually creates a reservoir that can supply water for irrigation and drinking. Water passes downward through a hydraulic turbine that is connected to a generator. Large plants, which depend on large volumes of water dammed upstream, can generate more than 2,000 MW. There are many small plants on rivers, some generating only a few hundred kilowatts. Among the largest plants in the United States are Hoover Dam and the Grand Coulee Dam. Hoover Dam has an installed capacity of 1,244 MW. Grand Coulee has an installed capacity of 2,025 MW. It is part of the Columbia River Basin project, which has a planned capacity of 9,770 MW.

The power produced by water depends upon the water's weight and head (height of fall). Each cubic meter of water weighs 1000 kilograms. For example, a column of water that is one meter square and one meter high would contain one cubic meter of water. It would press upon each square meter of turbine blade with a force of 1000 (1 x 1000) kilograms. Engineers measure waterpower in terms of watts (kilowatts or megawatts). One watt is the force it takes to raise one kilogram one meter in one second. The power potential of a waterfall is found by multiplying its flow, measured in cubic meter per second, by its height, measured in meter. Then the product is multiplied by 980, which is 1000 (the number of kilogram in a cubic meter of water) multiplied by 9.81(gravitational acceleration). For example, a 100-meter high waterfall with a flow of 10 cubic meter per second would develop 100 x 10 x 980, or 980,000, watts. The output of a hydroelectric plant is usually measured in kilowatts or megawatts of electricity.

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